Solve r = 1/2m^2p for p

You just have to arrange the equation such that the p is the only term at the left hand side of the equation. Express it in terms of r and m.

r = 1/2*m²*p

Divide both left and right hand side equations by 1/2*m²

p = r / (1/2 * m²)

Take the reciprocal of 1/2 and multiply it. The final answer is:

p = 2r/m²